The mermaid legend has been around since before the Romans ruled the earth, and even back then, guys were asking the same question: How did these womanly fish have sex?

It's a question that dogged filmmaker Charlie Foley when he started work on "Mermaid: The Body Found," a speculative documentary airing May 27 and 28 on Animal Planet -- from his own father, no less.

"It was the first thing my dad asked me when I told him about the special," Foley laughed to The Huffington Post. "We had to think about this, and I assume that mermaid sex organs would evolve like those of whales, seals and porpoises. Their bodies are streamlined, but those parts 'pop out' when needed."

Sorry, fish fetishists, the special doesn't show mermaids and mermen splashing around in icthyological intercourse, but there is a scene of a CGI mermaid giving birth.

Foley isn't saying that mermaids exist, but finds it fascinating that the comely sea creatures have been talked about for thousands of years and show up in the writings of numerous cultures -- even among cultures that had no contact with each other.

There has never been a confirmed mermaid sighting, and some researchers speculate that people who've claimed to have seen one outside of a movie theatre actually saw creatures like manatees or dugongs.

However, some researchers have suggested the "Aquatic Ape Theory." They claim that during a period of massive coastal flooding, some ancestors moved inland and others went into the ocean for food.

The theory forms the basis of the show and while the idea that mermaids might be real may sound absurd on the surface, filmmaker Charlie Foley says further study suggests it might not be all wet.

"There are cases of animals going from terrestrial to aquatic," Foley told The Huffington Post. "And when you look at what makes humans unique among other terrestrial animals, it raises some interesting questions on whether mermaids might be plausible."

MERMAIDS THROUGH THE AGES GALLERY (Story continues below)

PHOTO GALLERY

Mermaids Through The Ages

Some of the evidence that Foley said could conceivably suggest a missing mermaid link include webbing between fingers, something other primates don’t have and the loss of body hair (which would create drag in water).

Other evolutionary steps that suggest a sea creature cousin include the fact that humans are the only land animal with subcutaneous fat, which helps insulate whales, seals and dolphins from the cold, and breath control.

"Humans can hold their breath up to 20 minutes, longer than any other terrestrial animal," Foley said. "In fact, we're the only land animal with an instinctive ability to swim."

Foley is quick to point out that he doesn't necessarily believe that mermaids existed, but, as he did with a previous special, "Dragons: A Fantasy Made Real," wanted to "plausibly imagine them."

To do that, he had to think about how a real mermaid would actually look -- and it's wouldn't be a red head like Ariel the Little Mermaid at all.

"Evolutionarily speaking, hair would be the first to go because it's a drag underwater," he said. "Also, we thought about the coloring. Sea mammals tend to have countershading. They are lighter on what, in layman's terms, would be the belly and darker on the back. This is so they would blend in with the water if you're looking at them from above and would blend in with the sun shining through the water if you're looking at them from below."

Foley hopes the special gets people interested in the Aquatic Ape Theory, but also admits that his goal isn't to win converts to the idea.

"This is meant for entertainment," he laughed. "We didn't submit this for peer review."